Refrigeration control system



May 24, 1966 D. F. LEISHER, JR

REFRI GERATION CONTROL SYSTEM Filed Sept. 27, 1963 @N IOPISW PDOIFDU Om Nm INVENTOR. DONNAL F. I EISHER,JR. BY

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mommmmnzzou OPOE ATTORNEY United States Patent O 3,252,295 REFRIGERATION CONTROL SYSTEM Dounal F. Leisher, Jr., St. Louis, Mo., assignor to American Air Filter Company, luc., Louisville, Ky., a corporation of Delaware Filed Sept. 27, 1963, Ser. No. 312,057 4 Claims. (Cl. 62-209) Th-is invention relates to refrigeration control systems and in .particular to a control arrangement for a refrigeration system in which an air cooled condenser is su-bject, at times, to severely cold ambient temperatures.

An example of a particular installation of this character is found in the air conditioning equipment used in underground missile sites in geographic areas having severe winter weather. Because of the nature of vthe installations, operation of the refrigeration system is frequently required in the dead of winter when the ambient temperature of the air drawn upon yto cool the condenser may be well below F. While -a damper arrangement may be used to vary the quantity of low temperature air being delivered to the condenser, on occassion the refrigeration system is shut down for extended periods and `the condenser may then be exposed, in a non-operating condition, through leakage of air to very low air temperatures. When the system includes a low-side pressure cut-out arrangement, placing the refrigeration 4system in operation after such a shut down period is difficult because the low temperature condenser creates a low suction pressure condition shortly after starting, and the low pressure cut-out then operates to shut the system down.

The object of this invention is to remedy this diiculty in a simple, inexpensive manner.

In accordance with the invention, a switch is provided in parallel with the low pressure cut-out and is controlled in response to air temperature conditions which reflect the condenser temperature. Specifically, the switch is arranged to be closed in response to air temperatures adjacent the condenser having a value substantially below a temperature indicating normal operation of the condenser, and to be in an open position in response to temperatures above that value. Thus while the llow pressure cut-out switch is effectively removed lfrom the circuit under conditions in which the difficulty normally arises, after the refrigeration system has Ibeen operated for a period that the low pressure cut-out switch has closed in response to an adequate suction pressure, the parallel switch opens so that the low pressure cut-out can thereafter perform its normal function.

The drawing is a diagrammatic view of one example of a refrigerating system incorporating the invention.

Referring to the drawing, it will be apparent that the refrigerating system is in large part conventional. The electrically powered motor-compressor unit has its high pressu-re or discharge side connected by high pressure line 12 to the inlet of an air cooled condenser 14. The refrigerant outlet side of the condenser is connected by line 16 to a refrigerant flow control device 18 at the refrigerant inlet to the evaporator 20. The refrigerant outlet side of the condenser is `connected by line 16 to a refrigerant flow control device 18- at the refrigerant inlet to the evaporator 20. The refrigerant outlet of the evaporator is connected by a low side or suction line 22 back to the inlet of the motor-compressor unit 10.

Power for the motor driving the compressor is provided through electrical line 24 having a normally-closed low pressure cut-out switch 26 in the line as illustrated. As is conventional, switch 26 is controlled in accordance with the pressure existing in `suction pressure line 22 and transferred through line 28 to bellows 30.

A shuntcircuit around cut-out switch 26 is provided by line 32 having normally open switch 34 therein. Switch 34 is herein characterized as a ylow temperature starting switch and is controlled by bellows 36 connected to line 38 `and sensing bulb 40 adjacent the downstream side of `condenser 14.

rThe condenser 14-is mounted in an air duct system 42 which includes an air inlet 44 in communication with ambient air, fan means 46 Ifor creating a draft through the duct system and discharging air back to atmosphere, and a damper arrangement 48 operative to control the proportions o-f air through the passage in which the condenser 14 is disposed, and `the bypass passage, in accordance with the air-conditioning load andthe prevailing ambient temperature conditions. 'Phe direction of air flow through the duct system is as indicated by the arrows. It is to be understood that the illustrated duct systemV 42 and the particular arrangement of dampers and fan therein is simply an example of one arrangement, and other arrangementsl may be readily conceived by those skilled in the art. However, it is important that the sensing bulb 40 be located so that it is reasonably accurately reflects the temperature condition of .the condenser 14. One bulb location which is suitable for the purpose is as shown, where it is located on the downstream side of the condenser and reasonably close thereto. Thus when the refrigeration system is operating and air ows through the condenser, the bulb senses the normal operating condition of the condenser through the heated air, irrespective of the quantity of air used to cool the condense-r. When the refrigeration system is not operating, and there is no fan induced air flow through the duct system, the bulb will still indicate condenser temperature by being located relatively clcse to the condenser. Under any condition, the temperature of the air around the bulb 40 therefore reects the operating condition of the condenser.

In normal operation of the refri-gerating system, the low pressure cut-out switch 26 is closed since .the suction pressure in line 22 is well above the pressure Value (say 18 p.s.i.g.) at which the bellows 30 contra-cts suiciently to cause switch 26 to open. The low temperature starting switch 34 is normally open since `the air temperature sensed by the bulb 40 is well above the value (say 70 F.) which permits bellows 36 to contract sufliciently to close switch 34.

On those occasions when the refrigerating system is shut down and the ambient temperatu-re is very low, leakage of air through the damper system may result in the condenser 14 being exposed for an extended period of time to the low ambient temperatures. Since the bulb 40 also senses the same low temperatures, the switch 34 will close in responsethereto. When the refrigeration system is started, the low temperature of the condenser and refrigerant therein will result in the refrigerant inthe condenser having a correspondingly low pressure value. Consequently there-may be an insucient pressure differential across the control device 18 to give a pressure in evaporator 20 and suction line 22 which will maintain low pressure cut-out switch 26 in a closed position. Thus the reduced suction pressure in 4line 22 causes switch 26 to open. However, with switch 34 closed because of the low temperature o-f bulb 40 reilecting the low temperature condition of the condenser the compressor will continue to run until the suction pressure and head pressure build up to values where the cut-out switch 26 closes. The low temperature start switch 34 will remain closed after cut-out switch 26 closes until the temperature sensed by bulb 40 exceeds the value indicating the condenser ternperature is approaching its normal operating range.

While during restarting of refrigerating system the low pressure cut-out switch 26 is prevented from performing its function of terminating operation :of the system under conditions indicating a malfunction of the type would normally result in the low pressure cut-out switch opening,

it will lbe appreciated that during this time `the capacity of the refrigeration system is substantially reduced so that problems of equipment freeze up e. g., in the evaporator 20) are minimized during this period. Under periods of normal operation of the refrigerrating system the switch 34 is open so that the low pressure cut-out switch 26 is able to perform its function of terminating operation of the system when a malfunction of the character .to which it responds is detected.

The invention' claimed is:

1. In a refrigerating system including an air cooled condenser and having a low-side pressure cut-out vswitch in the electrical power l-ine to the compressondriving unit:

(a) a second separate and independent switch in said electrical power line in parallel with said cut-out switch;

(b) and means for controlling said second 'switch in response tothe downstream air temperature adjacent said condenser and reilecting the temperature of said condenser, said cont-rol means Iclosing said switch in response to downstream air temperature reflecting asubstantially reduced condenser temperature.

2. In a ref-rigerating system:

(a) an electrically powered compressor;

(b) an air cooled condenser in an air o'w passage;

(c) means to control the flow of cooling air through said passage;

(d) a normally closed low pressure cut-out switch in the electrical power line to said compressor;

(e) a second separate and independent switch in said electrical power line in parallel with said cut-out switch; and,

(f) air temperature responsive means located downstream of said condenser in said passage for controlling said second switch, said means operating said second switch to a closed position to complete a shunt circuit around said ycut-out switch in response to downstream air temperatures reflecting a substantiallly reduced condenser temperature.

3. In a refrigerating system including an electrically powered compressor', an air cooled condenser and an evaporator:

(a) a low pressure cut-out switch in the power circuit lfor said compressor;

(b) a shunt circuit in said power circuit around said cut-out switch including a second switch; and

(c) means directly responsive to the air temperature adjacent said downstream side of said condenser for operating said second switch to a closed position in response to said downstream air temperature reecting a substantially reduced condenser temperature.

4. In a refrigerating system including an electricallypowered compressor, an air-cooled condenser disposed in a passage having means to regulate air flo-w Ithrough said condenser; and an evaporator;

(a) a low pressure cut-out switch in the power circuit for said compressor;

(b) a shunt circuit around said cut-out switch including a second switch; and A (c) means responsive to the air temperature located in the air leaving side of said condenser `for operating said second switch .to a closed position in response to said air temperature reilecting a substantially reduced condenser temperature.

References Cited by the Examiner UNITED STATES PATENTS 2,267,607 12/1941 Harvey 62-209 MEYER PERLIN, Primary Examiner. 

1. IN A REFRIGERATING SYSTEM INCLUDING AN AIR COOLED CONDENSER AND HAVING A LOW-SIDE PRESSURE CUT-OUT SWITCH IN THE ELECTRICAL POWER LINE TO THE COMPRESSER DRIVING UNIT: (A) A SECOND SEPARATE AND INDEPENDENT SWITCH IN SAID ELECTRICAL POWER LINE IN PARALLEL WITH SAID CUT-OUT SWITCH; (B) AND MEANS FOR CONTROLLING SAID SECOND SWITCH IN RESPONSE TO THE DOWNSTREAM AIR TEMPERATURE ADJACENT SAID CONDENSER AND REFLECTING THE TEMPERATURE OF SAID CONDENSER, SAID CONTROL MEANS CLOSING SAID SWITCH IN RESPONSE TO DOWNSTREAM AIR TEMPERATURE REFLECTING A SUBSTANTIALLY REDUCED CONDENSER TEMPERATURE. 